Printing plates for use in offset printing



0a. 27-, 1959 D. H. COLES 2,

PRINTING PLATES FOR USE IN OFF SET PRINTING Filed Feb. ll. 1955 Fig.1

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.INVENTOR. DEREK HARRISON 6015s BY ATTORNEYJ' United States PatentPRINTING PLATES FOR USE IN OFFSET PRINTING Derek Harrison Coles, London,England Application February 11, 1953, Serial No. 336,402

5 Claims. (Cl. 96-33) The present invention relates to the production ofprinting plates for use in offset printing and is concerned with amethod of producing such plates of the type in which an original in theform of an image on a translucent or transparent carrier is transferredto a printing plate by making the plate sensitive to light, placing thecarrier in contact with the light-sensitive plate, directing lightthrough the carrier onto the sensitized plate, and subsequentlydeveloping the plate to form an offset printing plate. 1

According to the present invention, in producing an offset printingplate by a method of the type specified, the said image is initiallyproduced without lateral reversal on the face of the tissue of a sheetof duplex paper, the said face of the tissue is then afiixed to a faceof the said carrier, the backing sheet of the duplex paper is removed,the side of the carrier bearing the said tissue is placed in closecontact with the sensitized printing plate and light is directed throughthe carrier bearing the tissue on to the sensitized plate.

The term duplex paper used in this specification means a papercomprising a thin tissue paper sheet superimposed on, and removablysecured by an adhesive to a single heavier backing sheet.

The method according to the invention enables printing down to beeffected with the side of the carrier bearing the image in contact withthe light sensitized printing plate and the use of the duplex paperenables this to be effected quickly and easily and without the need forpreparating a laterally reversed image in the first instance.Furthermore the printing plate is produced Without the use of a cameraand dark room equipment and without the cost of making photographicnegatives or positives and retouching is unnecessary.

The carrier may conveniently be of paper such as baryta paper althoughinmany cases glass, a trans parent foil, or a translucent material such asa cellulose acetate film may be used alternatively. The instability offilm is well known and since this is not used as an intermediate step inreproducing the image onto the sensitized surface of the metal plate,the image will tend to remain more stable particularly if the carrier beof glass or a stable film such as the material known as Astrafoil. Theexposure time when using a paper carrier may be reduced by treating thepaper with a suitable oil. This has the further effect of improving thestability of the image.

The invention is particularly suitable for producing ofiset lithographicprinting plates.

The invention can be carried out as described by way of example withreference to the accompanying diagrammatic drawings in which:

i Fig. 1 illustrates a sheet of duplex paper in perspective with thetissue and backing sheet separated at one corner,

Figs. 2 to 9 inclusive are diagrams illustrating successive stages inthe'production of a printing plate, and

l ice Fig. 10 illustrates a variant of the method illustrated by Figs. 2to 9.

In the embodiment of the invention illustrated in Figs. 1 to 9 of thedrawings, the first step in the production of a printing plate for usein offset printing is to form the required opaque image, without lateralreversal, on the face of the tissue 11 of a sheet of duplex paper.

The tissue 11 is constituted by a thin sheet of tissue paper which issuperimposed on and removably secured by an adhesive to a heavierbacking sheet 12. In Fig. 1, the tissue 11 and backing sheet 12 of theduplex paper are shown separated at one corner.

One method of forming the above-mentioned opaque image is by printing,as follows. Type is set up and made ready on a letter-press machine. Apull is then taken on the tissue 11 of the sheet of duplex paper, usingany suitable printing ink which need not be black. As will be noted inFigs. 2 to 4 of the drawings, the ink which is applied to one surface ofthe tissue sheet in forming the image 11 thereon, is absorbed throughthe tissue sheet so that it extends to the other surface of the latter.A duplex paper which has been found to give satisfactory results is thepaper sold by Brittains Limited of Cheddleton Paper Mills, Near Leek,Stafiordshire, England, under the designation W.P.D.W. Paper. A proofthus obtained is next dusted over with black or metallic dusting powder,which may conveniently be lamp black, by dabbing lightly with cottonwool dipped in the powder. French chalk is then dusted over the surfacewith cotton wool, and the whole wiped clean with fresh cotton wool orbrushed oif with a soft brush. Thus the image '11 (Figs. 2 to 4) isrendered opaque.

The duplex paper is then affixed by means of an adhesive to a carriersheet 13 of baryta paper with the tissue side to the carrier sheet, asillustrated in Fig. 2. The TAPPI Monograph SeriesNo. 7, entitledPigments for Paper Coating and published 1948 by the TechnicalAssociation of the Pulp and Paper Industry, New York, N.Y., on pages14-16 thereof in an article entitled Barium Sulphate Pigments indicatesthat baryta paper is a paper coated with barium sulphate using a highgrade gelatin as the adhesive and refers to a discussion by Dr. Th.Bentzen on haryta paper in Tech. Assoc. Papers 8:4952 (1925) regardingthe fundamentals involved in the preparation of the coating mix, itsapplication to the raw stock'and the testing of the finished paper. Thisarticle also points out that barium sulphate is a heavy white pigmentwhich is formed from the mineral, barytes, occurring in the UnitedStates or witherito, a barium carbonate ore mined in Europe and England.According to this article, the barium sulphate coating on paper is adense compact film and does not take a high gloss but is useful for dullor matte finishes which have a characteristic satiny feel. As ishereinafter indicated the barium sulphate coating on the baryta paperprovides a good drawing or printing surface. Barium sulphate readilyabsorbs ink, without blurring like blotting paper. As a result of thesubstantial quantity of ink that this coating will absorb, the lines aredense and thus effectively interrupt the passage of light and produce asharp image on the printing plate.

The backing sheet of the duplex paper is now removed, leaving only thetissue 11 face down on the carrier sheet 13, see Fig. 3. The carriersheet 13 and the tissue 11 carried thereby are next rendered translucentby means of medicinal paraffin thinned with benzene, excess oil beingremoved with the aid of blotting paper.

An aluminium printing plate is then prepared with a 2%% solution ofglacial acetic acid, rinsed in water and coated in a whirler at say 60r.p. m. with a coating 15 'of gum arabic and ammonium dichlormatesolution.

When dry, the sensitized plate 14 so produced is placed in a printingdown frame with the carrier sheet 13 hearing the tissue 11 in closecontact with the coating 15, the side of the carrier sheet 13 hearingthe tissue 11 being placed in contact with the sensitized coating 15, asillus trated diagrammatically in Fig. 4.

The sensitized coating 15 on the plate 14 is then exposed. Fig. 5 showsthe plate after it has been exposed and after the carrier sheet 13 andtissue 11 have been removed. The exposed areas 16 have been hardened bythe action of the light whilst the unexposed areas 17 remain soft.

During the subsequent development, the unhardened areas 17 of thecoating are removed, leaving the exposed areas 16 in relief asillustrated in Fig. 6.

After developing the plate 14 with a developing solution such as oneconsisting of a solution of calcium chloride and lactic acid, the plate14 is etched from 2 to 4 minutes in a solution such as calcium chloride,zinc chloride, iron perchloride and hydrochloric acid with the resultthat the level of the uncoated portions of the plate is depressed as at18 (Fig. 7) below the level of the metal surface. When etching has beencompleted, the etching solution is removed with several applications ofwaterfree alcohol 200 proof and the plate is dried.

The plate 14 is then based with an azeotropic mixture and inked in withlithographic ink, so that the depressed areas 18 (Fig. 7) are therebycoated with ink as at 19 (Fig. 8). After French chalk has been applied,the lighthardened portions 16 of the coating are removed by rinsing orsoaking in warm water followed, if necessary, by light brushing. Whenthis operation has been completed, the plate is dried and is gummed andwashed out with asphaltum solution in the usual way. In the finishedplate those parts of the surface of the plate 14 from which the hardenedcoating 16 has been removed constitute metallic water-receptive areas 20between the inked printing areas 19.

In the example described above, the plate is developed (see Fig. 6 etseq.) by the deep etch process. The exposed plate can however bedeveloped by other known processes in which a laterally reversedpositive is normally used or could be used, such as for example the gumreversal process or the so-called Vandyck process.

It will be understood that the duplex paper, instead of being affixed tothe carrier sheet 13 by means of a separate coating of adhesive, mayalternatively be of the kind in which the tissue side is already gummedor coated with a thermoplastic adhesive.

An alternative method of forming the original opaque image on the faceof the tissue of the duplex paper, is to apply it by means of atypewriter or the like in the form of an ink impression having a tackyor greasy surface to which the lamp black subsequently dusted over itwill adhere.

The typewriter is preferably an electrically-operated typewriter ortype-setting machine capable of producing justified lines of copy, suchas any one of the typewriters sold under the following trade marks andtrade descriptions: Orotype, Vari-Typer, I.B.M. Typewriter, Justowriter,Lithotype and Underwood Justifying Typewriter. An ordinary typewriter ofthe kind now widely used at the present time may, however, be used.

Any ribbon used for typing direct onto an offset plate for duplicatingwould be found suitable for use in those cases where the typeimpressions are struck with a ribbon.

In the case of machines which operatewith one time paper ribbons, theribbon may be a paper ribbon coated with soft, greasy carbon.

The image can alternatively be drawn or written with an opaque ink whichwould not require subsequent dustmg.

The subsequent procedure is the same as that already described withreference to Figs. 2 to 9.

It will be apparent to those skilled in the art that the invention mayalso be applied to the production of a series of offset printing platesfor reproducing coloured images. The several colour component images areformed on the tissue of duplex paper without lateral reversal andtransferred to a suitable carrier as in the example already described.This is particularly suitable for adapting a series of letterpresscolour blocks for lithographic printing. The letterpress colour blocksmay be used to form images on the tissue of duplex paper and the imagesmay be transferred to offset lithographic printing plates in the manneralready described.

Furthermore a duplicate offset lithographic printing plate can readilybe produced from an existing plate by employing the existing plate toprint an image on the tissue of a sheet of duplex paper. The image maybe transferred from the duplex paper to an offset lithographic printingplate in the manner already described.

The invention may also be employed to add type, a drawing or other imageto an existing positive or photographic transparency for use inproducing an offset lithographic printing plate.

If it is required to reverse the original that is to print a white imageon a black or coloured background from the original black image on whitebackground the sensitised coating on the lithographic printing platewill be other than that described and may be, for example, the wellknown emulsion containing egg albumen, ammonium dichromate and water.The areas of emulsion not exposed to light are washed out duringdeveloping.

The invention may be used with advantage in producing offset printingplates for printing images formed partly of lines and partly of words orsymbols. For

example, it can be used for printing musical compositions or businessforms consisting of lines with box headings. In such cases, it willgenerally be desirable to apply the image to the duplex paper or to theduplex paper and carrier sheet in two separate operations. For example,the staves may first be printed without lateral reversal on the face ofa tissue of the duplex paper which is then fixed to the face of thecarrier, after which the backing sheet is removed. The musical notationsmay then be superimposed in a similar manner in the required positionsin relation to the staves on to the above-mentioned tissue, the backingbeing thereafter removed to producev a laterally reversed positivecombining both parts of the image to be printed.

Alternatively, the lines or staves may be printed or drawn laterallyreversed on the carrier sheet, to which the face of the tissue of theduplex paper is to be affixed subsequently, and the notes, box headingsand the like drawn or printed without lateral reversal on the face ofthe tissue and stuck in the required positions, on the face of thecarrier or vice versa.

In Fig. 10, which illustrates this variant, 21 represents the laterallyreversed lines or staves on the carrier sheet,

While the other references indicate parts corresponding.

to those bearing the same references in Fig. 4. The caliper of thetissue is such that it is insuificient to cause distortion by lightdiffusion or creep and will not aided the clear reproduction of thelines or staves 21.

The last-mentioned procedure may be used with appropriate modificationsfor producing images in the form of lines and box headings, such as arerequired in busi-- Although particular reference has been made to thethese may be of paper.

production of offset lithographic printing plates, it will be understoodthat the method according to the invention can also be used in theproduction of photogravure plates or cylinders or any other process,such as offset-letterpress or dry oifset lithography where a reversedpositive can be used. Furthermore although reference has been made to analuminum plate it will be understood that plates of other materials suchas zinc, copper, magnesium, tri-metal and bi-metal with the appropriatechemicals, may also be employed.

The invention facilitates storage of originals since Furthermore, in theevent of say a first edition of a book being made and it being desiredto ensure that a second edition can be printed later, the letterpresstype or the plates themselves need not be kept neither need theoriginals. All that is required is that a duplicate set of duplex papersbe produced taking care that both sets are dusted with the opaque powderbefore they are dry. The duplicate set may then be stored indefinitelyin a dry place and may be used at any later date to prepare a fresh setof printing plates. Thus the plates or type used for the first editionmay be melted down and used again. A duplicate set of duplex papers isalso easily transportable. An additional advantage is that thesignatures of the book have the pages already imposed in the correctposition for subsequent printing.

While the invention has been described above by way of example withreference to line subjects, it should be understood that it is equallyapplicable for the reproduction of half-tones.

I claim:

1. The method of producing a printing plate for use in offset printing,which comprises taking a duplex paper composed of a thin tissue papersheet removably secured throughout its entire area by adhesive to abacking sheet of heavier paper and applying to the outer surface of thetissue sheet of such duplex paper an opaque right-reading image of partof an original to be transferred to a printing plate, applying to apaper carrier sheet a laterally reversed image of another part of saidoriginal, securing such outer surface of the tissue sheet of the duplexpaper to the image bearing surface of said carrier sheet so that bothparts of such image are sandwiched therebetween, separating the backingsheet of the duplex paper from the tissue sheet thereof, leaving thetissue sheet adhered to the carrier sheet with the image therebetween,rendering the paper carrier sheet capable of transmitting light raystherethrough, placing the other surface of the tissue sheet in closecontact with the light sensitive material of a sensitized printingplate, then directing light through both the carrier and tissue sheetsand onto the light sensitive material of such printing plate, and thendeveloping and cleaning said printing plate.

2. The method of producing a printing plate for use in offset printing,which comprises taking a duplex paper composed of a backing sheet towhich a thin tissue paper sheet is removably secured throughout itsentire area by an adhesive and applying a right-reading image to theouter surface of the tissue sheet of such duplex paper, applying to onesurface of a carrier constituted of material capable of transmittinglight rays therethrough a second laterally reversed image, then securingthe outer surface of the tissue sheet of the duplex paper to said onesurface of said carrier so that said right-reading image and saidlaterally reversed image are both sandwiched between the tissue sheetand the carrier, separating the backing sheet of the duplex paper fromthe tissue sheet thereof, leaving the tissue sheet adhered to thecarrier with the images therebetween, placing the other surface of thetissue sheet in close contact with the light sensitive material of asensitized printing plate, and then directing light through both thecarrier and the tissue sheet and onto the light sensitive material ofsuch printing plate,

whereby the matter of both images is combined on the finished printingplate.

3. The method of producing a printing plate for use in offset printing,which comprises taking a duplex paper composed of a thin tissue papersheet removably secured, throughout the area thereof to which an imageis to be applied, to a backing sheet of stiffer material and applying tothe outer surface of the tissue sheet thereof in such area and with inkan original in the form of a rightreading image, dusting the outersurface of the tissue sheet with an opaque powder before the ink is dry,removing the powder except where it adheres to the ink, adhering suchouter surface of the tissue sheet to a surface of a sheet of barytapaper, stripping said backing sheet from the tissue sheet leaving thelatter adhered to the baryta paper, increasing the translucency of thecomposite baryta and tissue paper in the image bearing area thereof bythe application of oil, placing the other surface of the tissue sheet incontact with the light sensitive material of a sensitized printingplate, and then directing light through both the baryta paper and tissuesheet and onto such light sensitive material.

4. The method of producing a printing plate for use in offset printing,which comprises taking a duplex paper composed of a thin tissue papersheet removably secured, throughout the area thereof to which an imageis to be applied, to a backing sheet of stiffer material andmechanically applying to the outer surface of the tissue sheet thereofin such area an original in the form of an opaque right-reading image,adhering such outer surface of the tissue sheet to a surface of a sheetof baryta paper, stripping said backing sheet from the tissue sheetleaving the latter adhered to the baryta paper, increasing thetranslucency of the composite baryta and tissue paper in the imagebearing area thereof by the application of oil, placing the othersurface of the tissue sheet in contact with the light sensitivematerialof a sensitized printing plate, and then directing light throughboth the baryta paper and tissue sheet and onto such light sensitivematerial.

5. The method of producing a printing plate for use in ofiset printing,which comprises taking a duplex paper composed of a thin tissue papersheet removably secured, throughout the area thereof to which an imageis to be applied, to a backing sheet of stiffer material andmechanically applying to the outer surface of the tissue sheet thereofin such area an original in the form of an opaque right-reading imageusing an ink that is capable of being absorbed through the tissue sheetso that such image extends to the other surface of said tissue sheet,adhering such outer surface of the tissue sheet to a surface of acarrier constituted of a sheet of baryta paper having substantiallygreater stiffness and strength than the paper of the tissue sheet,stripping said backing sheet from the tissue sheet leaving the latteradhered to the carrier baryta sheet, increasing the translucency of thebaryta sheet by the application of oil, placing the other surface of thetissue sheet in contact with the light sensitive material of asensitized printing plate and with the inner surface of said imageagainst such light sensitive material to substantially eliminate lightcreep, and then directing light through both the oiled baryta and tissuesheets and onto such light sensitive material in the area of said sheetsin which the outer surface of said image at the outer surface of saidtissue sheet is not opposed to such directed light.

References Cited in the file of this patent UNITED STATES PATENTS729,803 St. John June 2, 1903 971,009 Ippers Sept. 20, 1910 (Otherreferences on following page) 7 UNITED STATES PATENTS Seyfierth July 1,1924 Wheelright Oct. 15, 1935 Buckingham Jan. 30, 1951 FOREIGN PATENTSGreat Britain of 1895 8 OTHER REFERENCES Modern Photoengraving, byFlader, pub. Modern Photoengraving, 1948, page 167. G.P.O., TransparentProofs from Type Forms, Bulletin C3, Government Printing Oflice, 1951,pages 1-18.

G.P.O., Transparent Proofs from Type Forms, Bulletin C-3, GovernmentPrinting Oflice, 1951, pages 1-2.

4. THE METHOD OF PRODUCING A PRINTING PLATE FOR USE IN OFFSET PRINTING,WHICH COMPRISINGS TAKING A DUPLEX PAPER COMPOSED OF A THIN TISSUE PAPERSHEET REMOVABLY SECURED, THROUGHOUT THE AREA THEREOF TO WHICH AN IMAGEIS TO BE APPLIED, TO A BACKING SHEET OF STIFFER MATERIAL ANDMECHANICALLY APPLYING TO THE OUTER STIFFER MATERIAL AND SHEET THEREOF INSUCH AREA AN OPRIGINAL IN THE FORM OF AN OPAQUE RIGHT-READING IMAGE,ADHERING SUCH OUTER SURFACE OF THE TISSUE SHEET TO A SURFACE OF A SHEETOF BARYTA PAPER, STRIPPING SAID BACKING SHEET FROM THE TISSUE SHEETLEAVING THE LATTER ADHERED TO THE BARYTA PAPER, INCREASING TRHETRANSLUCENCY OF THE COMPOSITE BARYTA AND TISSUE PAPER IN THE IMAGEBEARING AREA THEREOF BY THE APPLICATION OF OIL PLACING THE OTHER SURFACEOF THE TISSUE SHEET IN CONTACT WITH THE LIGHT SENSITIVE MATERIAL OF ASENSITIZED PRINTING PLATE, AND THEN DIRECTING LIGHT THROUGH BOTH THEBARYTA PAPER AND TISSUE SHEET AND ONTO SUCH LIGHT SENSITIVE MATERIAL